Present day sailcloth is made from a variety of materials, with one of the most common being a tightly woven cloth of polyester yarns. Sailcloth is the most tightly woven textile in the world and requires extensively modified heavy looms to generate the necessary forces to attain such a dense construction. Normally, polyester sailcloth is only woven in what is known as a plain weave, in which every warp yarn passes over and under each fill yarn, with the yarns being crimped over each other. After weaving, the cloth is impregnated with a resin and is heated, causing the resin to cure and also causing the polyester fabric to shrink.
The above described weaving method tends to impart certain characteristics to the cloth due to the nature of the operation itself. The warp yarns, which run in the machine on long direction tend to crimp more than the weft or fill yarns, which run in the cross machine direction. Sails of this nature are made up of a number of joined panels, and it is desirable to align the yarns with less crimp along directions of maximum stress or load in the sail. This, in turn, reduces stretch, which would otherwise cause the sail to lose its ideal or designed shape when subjected to increasing wind forces.
Fill oriented cloth imposes limitations on how panels can be cut and arranged in a sail while still making efficient use of the cloth. A common design using fill oriented cloth is a so-called cross cut design, in which the seams are substantially horizontal, and the fill yarns run from the top to the bottom of the sail.
Studies of the properties of sails have demonstrated that in triangular sails, especially genoas or jibs, the main forces radiate out of the corners of the sail. It becomes desirable to have sail panels which radiate out of the corners of the sail, and the most efficient way to accomplish this is with warp oriented cloth, e.g., cloth in which the warp yarns are relatively uncrimped.
One proposed solution to manufacture warp oriented polyester sailcloth is simply lower or reduce the fill yarn density by reducing or decreasing the fill yarn count per inch, thus increasing the spacing between the fill yarns. This approach is technically inferior for at least two reasons. The lower fill count significantly reduces the diagonal stability of the cloth, causing undesirable increased stretch along the bias. Also, lowering the fill count only partially reduces crimp in the warp yarns and also reduces the density of the weave. Thus, the cloth can still stretch in the warp direction and has a low service life.
In current fill oriented woven polyester fabrics, the natural tendency of the warp to crimp more than the fill is accentuated by using larger (heavier) fill yarns than warp yarns. The ratio of fill yarn weight to warp yarn weight is typically between 1.67 to 1 and 4.5 to 1. The density of these fabrics (as later defined herein) are in the order of 1,500 to 2,050 in the warp and from 1,000 to 1,330 in the fill.
In accordance with the present invention a novel woven fabric of polyester or other heat shrinkable yarn is provided with yarn orientation in the warp direction, that is, crimp is imparted to the fill yarns while leaving the warp yarns relatively uncrimped, and also while producing the desired high fiber density fabric. This is accomplished by increasing the spacing between warp yarns to levels higher than current conventional fabrics and reversing the yarn weight ratios (fill vs. warp) to values between 1.0 to 1 and 0.22 to 1. This provides densities (as defined herein) in the warp of 970 to 1,500 and in the fill of greater than 1,400. The resulting cloth is then finished in a conventional fashion and is ready to be cut into panels.